Fair Value - Schedule of fair value measurements (Details) - Fair value, recurring - USD ($) $ in Thousands	Sep. 26, 2020	Sep. 28, 2019
Level 1 | Short-duration bond fund (Level 1) (1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 407,784	$ 0
Level 2 | Commercial paper (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	42,500
Money market funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value disclosure	$ 310,569	$ 0